The invention relates, in general, to flow measurement and flow meters, and, more particularly, to a new and useful method for vortex shedding flow measurement.
Vortex shedding flow measurement deals with the eddies or vortices which shed from an obstruction, known as a bluff body or strut, which is placed in the path of a flow stream. As the flow stream contacts the bluff body, the surface layer separates from opposite sides of the bluff body. Shedding alternatingly occurs at both of the opposite sides. The vortex shedding frequency is proportional to the flow rate across the bluff body.
In known vortex shedding arrangements, the differential pressure induced by vortex shedding has been sensed by a variety of monostable analog elements. Among these elements are diaphragms which deflect proportional to the differential pressure, the deflection of the bluff body itself or a secondary body due to the pressure drop, or fluid flow which is induced due to this differential. A disadvantage of these sensing means is that the frequency of vortex shedding is proportional to flow rate as well as the amplitude of the differential pressure pulse. Therefore, at low flow rates the output of an analog sensor can be too low to measure.